Directions: top 0, right 1, bottom 2, left 3

The set of rotation values are the same as directions.

The maze symbol (has four edges) bit-packed in charMap as 2^d per direction, mirrored in shiftL 4 to help bit rotation

X – ╋          -- 4 edges
I – ━, ┃       -- 2 edges
L – ┏, ┛, ┓, ┗ -- 2 edges
T – ┣, ┫, ┳, ┻ -- 3 edges
i – ╸, ╹, ╺, ╻ -- 1 edge

Mutable maze operated on by functions in section "Maze operations"

Choices is bit-packed info related to the valid rotations of a picce. In MSB order: (valid) rotation count 2b, invalid rotation directions 4b (unused), solved requirements 4b, solved neighbours 4b

PartId distinguishes the graph component by their smallest known Cursor by its Ord (unique), so it is the same as its cursor initially. They're marked in origin ahead of solveds. PartId in origin is only to be used through partEquate, because origin isn't being updated after components have connected.

Continue represents the piece that should be solved next according to Priority, which is an open end of a component (or starts one). Created in initProgress or deltaContinue.

Continue priority queue, inserted by prioritizeContinue, found by findContinue, popped by popContinue.

Primary storage of Continue data

The index of components' continues by their PartId (which are always up-to-date).

For backtracking on the mutable MMaze and for extracting hints.

Island is the patch of unsolved pieces surrounded by solved pieces, computed by flood in islands.

IslandSolution represent a solution for an island with a representative progress. The icConnections are a partition of the components the island joined. Partitions have a partial ordering called _refinement_ with which you can group iSolutions. https://en.wikipedia.org/wiki/Partition_of_a_set#Refinement_of_partitions

Amalgamation of the flags "determinstic", "save history" and "deprioritize unbounded continues" (it's for parallelism, see rescoreContinue).

Connects PartIds on the board

Looks up the fixed point of PartId (i.e. when it points to itself)

Print unicode maze with colorized ANSI escape sequences to stdout.

Generate uncolorized output

The output format is: images/lvl%i-%s-%0*i-%s.png level mazeId (sizeLen iter) name

Tracing at each freq= step with debug= environment variables.

Modes: 1. print stats / 2. print maze with terminal escape code codes / 3. as 2., but with clear-screen before / 4. as 1., but with image output / 5. as 4., but only after islands have started

directions = rotations = [0, 1, 2, 3]

This accounts for some piece's rotational symmetry

Rotates the Pix to left by n Rotations

Compute initial rotation fields for a piece's Choices

Calls prioritizeContinue on nearby pieces (delta = 1)

Recalculates the Continues score, less is better (because of deleteFindMin in findContinue).

score = (0 - island << 17 + (choices << (15 - choicesCount)) + x + y) << 32 + created

Inserts or reprioritizes Continue

Check if Continue is about to become separated from the rest of the graph.

Pops priority by score, deletes from continues.

Pops next Continue from queue.

The generic paint of the flood fill.

Four-way flood fill with FillNext as the "paint". The initial piece is assumed to be valid FillNext.

Set low priority to all continues with island = 1.

Computes and set iChoices/iSolutions for the island, but also modifies maze with icHints if len choices == 1.

Solves a valid piece, mutates the maze and sets unwind. Inefficient access: partEquate reads the same data as islands reads. (All functions within this function are inlined)

The initial Progress, space stack, Progress and MMaze backtracking operations. This returns a progress with the first available Continue from space or Nothing. If space is empty, it gets popped, mazePop gets called and it tries again until space is empty.

Solves pieces by backtracking, stops when the maze is solved or constraints met.

Sovles deterministic parts of the maze in parallel.

Solver main, returns solved maze

Create Configuration from environment variables, create image output directory.

Gets passwords for solved levels from the maze server.

Run solver, likely produce trace output and complain if solve is invalid (verify).

Executable entry point.